1. Field of the Invention
The invention relates to a process and an apparatus for producing endless laminated veneer boards.
2. Description of the Related Art
A process for producing laminated veneer boards has been disclosed in DE-A 196 27 024. That process is based on the object of combining laminated assemblies of large-area veneer panels (or sheets) automatically and continuously with adequate mechanical connection so that, given the subsequent continuous pressing operation, the veneer-assembly transition points have virtually the same physical strength properties in the finished laminated veneer boards as the laminated veneer boards produced according to the previous laminated veneer assemblies of sandwich construction. Thus, it is possible to produce laminated veneer boards of good quality if all of the manufacturing or production parameters are matched to one another in an optimum manner and the apparatus operates accordingly. Problems arise, however, from the fact that the moisture content of the layers of glue on the surfaces of the veneer panels and the moisture content of the veneer panels themselves are either too low or too high. If the moisture content is too high, there is the risk that an air/vapor mixture will lead to the formation of vapor in capillaries, resulting in splits in the finished product. If the moisture content is too low, the resulting strength properties of the laminated veneer boards are inadequate. With regards to process engineering, heat transfer to the center, as in the production of particle board and fiber board, is not possible in the course of vapor generation during the production of plywood or LVL boards, because the veneer panels form a natural vapor barrier.
The object of the present invention is to specify a process and an apparatus by means of which higher quality and a higher throughput rate (through a faster sequence) can be achieved in the continuous production of laminated veneer boards.
According to a first embodiment of the process according to the invention, a method of producing endless laminated veneer boards comprises the steps of: applying an adhesive to at least some of a plurality of veneer panels; assembling the plurality of veneer panels in a plurality of interlinking layers to form one or more cover-layer strands, each of the cover-layer strands having central panels and outer panels; combining one or more of the plurality of cover-layer strands to form a veneer-panel strand, the veneer-panel strand having outer layers and central layers, wherein a moisture content of at least one of the adhesive and the veneer panels is greater at the central layers than at the outer layers; and preheating said veneer-panel strand from inside outwards.
Preferably, the central layers have a moisture content of about 7.8%, and the outer layers have a moisture content of about 6%.
The method may further comprise the step of pressing the veneer-panel strand in an operating press.
Further, during the step of assembling, direction of fibers in one of the plurality of layers of the veneer panels may be placed at a 90xc2x0 offset to an adjacent layer.
A derived timber product board strip may be combined between two cover-layer strands. The derived timber product board strip may be a particle board strip, MDF fiber board strip or OSB fiber board strip.
According to a second embodiment of the process according to the invention, a method of producing endless laminated veneer boards comprises the steps of: applying an adhesive to at least some of a plurality of veneer panels; assembling the plurality of veneer panels in a plurality of interlinking layers to form one or more cover-layer strands, each of the cover-layer strands having central panels and outer panels; combining one or more of the plurality of cover-layer strands to form a veneer-panel strand, the veneer-panel strand having outer layers and central layers, wherein a moisture content of at least one of the adhesive and the veneer panels is lower at the central layers than at the outer layers; and preheating said veneer-panel strand from outside inwards.
Preferably, the central layers have a moisture content of about 6%, and the outer layers have a moisture content of about 7%.
According to a third embodiment of the invention, an apparatus for producing endless laminated veneer boards, comprises: at least one adhesive applicator for applying adhesive to veneer panels; at least one veneer-panel laying device for interlinking layers of said veneer panels to form a cover-layer strand; and a preliminary press with preheating device for preheating from inside outwards a veneer-panel strand comprising one or more of said cover-layer strands, said veneer-panel strand having outer layers and central layers, wherein a moisture content of at least one of the adhesive and the veneer panels is greater at the central layers than at the outer layers.
The apparatus may further comprise a controller for numerically controlling release or engagement of gluing rolls in the adhesive applicator during passage of the veneer panels.